Hot-Rolled Flat Steel Product and Method For the Production Thereof

• Main Authors: HISKER FRANK, HELLER THOMAS, KORPALA GRZEGORZ, HAMMER BRIGITTE, KAWALLA RUDOLF
• Format: Patent
• Language: English
• Published: 23.07.2015
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; TREATMENT OF ALLOYS OR NON-FERROUS METALS

A hot-rolled flat steel product having a product of Rm and A80 of 18,000 MPa*%, a composition including (in wt.) C:0.10-0.60%, Si:0.4-2.0%, Al: 2.0%, Mn:0.4-2.5%, Ni: 1%, Cu: 2.0%, Mo: 0.4%, Cr 2%, Ii: 0.2%, Nb: 0.2%, V: 0.5%, remainder Fe and unavoidable impurities, and a microstructure of bainite and residual austenite, wherein the microstructure includes 60 vol.% bainite, and wherein at least some of the residual austenite is in block form and 98% of the residual austenite blocks have a size of 5 μm. Also, a method where a slab, thin slab or a cast strip having the aforementioned composition is hot-rolled at a hot-rolling end temperature of 880° C., cooled with a cooling rate of 5° C./s to a coiling temperature between the martensite start temperature and 600° C., coiled, and cooled in the coil while being held between the bainite start temperature and the martensite start temperature until 60 vol.% of the hot strip microstructure is bainite.